Preparation method of zinc oxide micro-nano powder through electrochemical pulse deposition and application of micro-nano powder obtained through method

Abstract

The invention provides a method for preparing zinc oxide micro-nano powder by electrochemical pulse deposition, which comprises the following steps: firstly, treating carbon nanofiber paper CNFs with strong acid, then forming a three-electrode electrochemical system by using a Pt counter electrode, an Ag / AgCl reference electrode and a treated carbon nanofiber paper working electrode, and preparing zinc oxide micro-nano powder by using a zinc nitrate solution as electrolyte. And zinc oxide micro-nano powder is obtained on the surface of the working electrode through an electrochemical pulse deposition method. The invention also provides an application of the micro-nano powder in latent fingerprint development. The preparation method is simple and environment-friendly, the used materials are safe and non-toxic, and chemical pretreatment is not needed; the obtained zinc oxide micro-nano powder has high sensitivity, can clearly display latent fingerprints on a complex object, has obvious detail characteristics including mastoid lines, fingerprint triangles and the like, can effectively avoid material evidence pollution, and is easy to popularize and apply.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of latent fingerprint development, and particularly relates to a preparation method of zinc oxide micro-nano powder and application of the zinc oxide micro-nano powder in latent fingerprint development. BACKGROUND

[0002] The existing latent fingerprint development technologies mainly include chemical methods (such as indantrione method and silver nitrate method), physical methods (such as powder brush development method) and optical methods (such as laser excitation).

[0003] Chinese patent application CN 101485571A discloses a technical solution for developing latent fingerprints by using ZnO doped MnO2 nanoparticles (ZnO / Mn), ZnO doped V2O5 nanoparticles (ZnO / V) or ZnO doped Ag nanoparticles (ZnO / Ag), which can be applied to surfaces such as glass, paper and table. Chinese patent application CN 101953690A discloses a method for developing latent fingerprints by using zinc sulfide and zinc oxide nanoparticles, which needs to prepare ZnO / Ag core-shell structure nanoparticle powder first, then disperse it in ethanol, immerse the test material in the dispersion liquid, and then perform optical imaging. Chinese patent application CN 1104382600A discloses a two-step latent fingerprint development method based on nanoparticles, which needs to prepare nanoparticle development liquid and fluorescent dye colorant respectively, then immerse the test material in the emulsion containing the nanoparticle development liquid, take out the test material and dry it, and then color it with the fluorescent dye colorant.

[0004] Obviously, these existing common technologies have technical defects, such as CN 101485571A, which has the problem of insufficient sensitivity: poor development effect on latent fingerprints on old, complex background or special materials (such as leather and RMB); such as CN 101953690A, which has the problem of high operation hazard: some chemical reagents (such as ethyl cyanoacrylate) are toxic, and the dust or gas generated during operation is harmful to the human body; such as CN 101953690A and CN 1104382600A, which have the problem of damaging the evidence: the actual development technology directly pollutes or damages the fingerprint residues, affecting the subsequent DNA extraction and inspection and identification.

[0005] Therefore, there is an urgent need in the field for a new method that can realize non-destructive development of latent traces, especially latent fingerprints. SUMMARY

[0006] The purpose of the present application is to overcome the defects of the prior art and provide a new micro-nano material that can be used for non-destructive development of latent traces, especially latent fingerprints.

[0007] To this end, the present application provides a preparation method of electrochemical pulse deposited zinc oxide micro-nano powder, which comprises the following steps:

[0008] (1) Pretreatment of carbon nanofiber paper CNFs

[0009] The clean carbon nanofiber paper CNFs is immersed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid for 4 hours, and then washed with deionized water to obtain the pretreated carbon nanofiber paper CNFs.

[0010] (2) Configuration of three-electrode electrochemical system

[0011] The Pt counter electrode, the Ag / AgCl reference electrode and the pretreated carbon nanofiber paper CNFs are combined to form a three-electrode electrochemical system, and the Zn(NO3)2 solution is used as the electrolyte.

[0012] (3) Electrochemical pulse deposition

[0013] The ZnO micro-nano powder is obtained on the surface of the carbon nanofiber paper CNFs by electrochemical pulse deposition under the conditions of an open potential of-1.7 V to-1.9 V, a closed potential of-0.8 V, a ratio of open time to closed time of 1: (1-100), and electrolyte heating.

[0014] The carbon nanofiber CNF is a non-continuous structural fiber material formed by stacking nanoscale graphite sheets, and the paper-like material prepared by using such fibers is the carbon nanofiber paper CNFs. The preparation method of such material is recorded in the prior art, for example, refer to Chinese invention patent CN 103015256B, and it can also be directly purchased from the market.

[0015] In the present application, the clean carbon nanofiber paper CNFs is cleaned by acetone, alcohol and deionized water, respectively.

[0016] Preferably, the mixed acid solution contains concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, wherein the mass percentage of concentrated sulfuric acid is 98%, and the mass percentage of concentrated nitric acid is 68%.

[0017] In the present application, the concentration of the electrolyte is generally not strictly required, and those skilled in the art can adjust the concentration of the electrolyte according to the electrochemical system. Generally, the Zn(NO3)2 solution (concentration of 0.05 mol / L, pH value of 5.26) directly purchased can achieve the technical scheme of the present application.

[0018] In the present application, different opening voltages and different pulse duty cycles can affect the crystal structure of the deposited zinc oxide micro-nano powder, so that the obtained powder has different surface morphologies, such as hexagonal column structure, flower-like structure, symmetrical pyramid structure, nanowire, etc. These different crystal structures can affect the photoluminescence properties. In the above step (3), under the conditions of an opening potential of-1.8 V, a closing potential of-0.8 V, a ratio of opening and closing times of (1-20), and 70℃, the zinc oxide micro-nano powder is obtained on the surface of the carbon nanofiber paper CNFs by the electrochemical pulse deposition method. The flower-like structure is observed under a microscope, and the zinc oxide micro-nano powder has a significant photoluminescence phenomenon under the excitation of 350 nm ultraviolet light, and is particularly suitable for developing latent fingerprints.

[0019] The electrochemical pulse deposition of the present application is carried out in a CHI660D workstation.

[0020] The particle size distribution of the zinc oxide micro-nano powder obtained by the preparation method of the present application is 200 nm-2 μm.

[0021] The present application also provides the use of the zinc oxide micro-nano powder prepared by the above preparation method in the development of latent fingerprints.

[0022] Based on this, the present application also provides a method for developing latent fingerprints using zinc oxide micro-nano powder, which comprises the following steps:

[0023] (1) Attaching the zinc oxide micro-nano powder on an object with latent fingerprints;

[0024] (2) Irradiating the area on the object where the zinc oxide micro-nano powder is attached with excitation light to obtain a latent fingerprint image.

[0025] The method of the present application can be applied to wooden material objects or metal material objects.

[0026] Preferably, the wavelength of the excitation light is 350 nm-700 nm.

[0027] The preparation method of the present application is simple and environmentally friendly, the materials used are safe and non-toxic, and no chemical pretreatment is required; the obtained zinc oxide micro-nano powder has high sensitivity, can clearly develop latent fingerprints on complex objects (such as dark wood and conductive aluminum foil), contains obvious details such as papillary lines and fingerprint triangles, and does not need to be soaked in reagents, effectively avoiding the pollution of physical evidence or the harm to human body caused by reagents; the latent fingerprint development method of the present application is simple to operate, the laser parameters used are adjustable, suitable for different scene requirements, compatible with existing physical evidence discovery equipment (such as laser full-scan instrument), and easy to popularize and apply. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Fig. 1-1 is a micro-morphology chart of carbon nanofiber paper;

[0030] Fig. 2-1 is a product obtained by using an opening potential of -1.7 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:5;

[0031] Fig. 2-2 is a product obtained by using an opening potential of -1.7 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:50;

[0032] Fig. 2-3 is a product obtained by using an opening potential of -1.7 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:100;

[0033] Fig. 2-4 is a product obtained by using an opening potential of -1.8 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:20, respectively;

[0034] Fig. 2-5 is a product obtained by using an opening potential of -1.8 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:50, respectively;

[0035] Fig. 2-6 is a product obtained by using an opening potential of -1.8 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:100;

[0036] Fig. 2-7 is a product obtained by using an opening potential of -1.9 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:10, respectively;

[0037] Fig. 2-8 is a product obtained by using an opening potential of -1.9 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:50, respectively;

[0038] Fig. 2-9 is a product obtained by using an opening potential of -1.9 V, a closing potential of -0.8 V, and a ratio of opening time to closing time of 1:100, respectively;

[0039] Fig. 3-1 is an XRD chart of samples No. 3, 4 and 8 of Example 1;

[0040] Fig. 3-2 is a fluorescence spectrum (PL) chart of some samples of Example 1;

[0041] Fig. 4-1 is a result of imaging a latent fingerprint on an aluminum foil sample in Example 2;

[0042] Fig. 4-2 is a result of imaging a latent fingerprint on a wood sample in Example 3. DETAILED DESCRIPTION

[0044] The following examples are used to non-limitingly explain the technical solutions of the present application.

[0045] In the present application, unless otherwise specified, "%" used to explain the concentration is mass percentage, and ":" is mass ratio.

[0046] The reagents and equipment used in the present application are commercially available products, and the specific sources are as follows: 0.05 mol / L Zn(NO3)2(pH value is 5.26), Tianjin Fengchen Chemical Reagent Technology Co., Ltd.; carbon nanofiber paper (CNFs) paper, Kunming Natai Technology Co., Ltd.; CHI660D workstation, Shanghai Chenhua Instrument Co., Ltd.

[0047] Example 1 Preparation of zinc oxide micro-nano powder

[0048] Take the carbon nanofiber paper CNFs paper (as shown in Figure 1 ), and wash it with acetone, alcohol and deionized water respectively, and dry it naturally. Then, immerse the carbon nanofiber paper CNFs paper in a mixed acid solution of concentrated sulfuric acid (98%) and concentrated nitric acid (68%) at a volume ratio of 3:1 for 4 hours. After the reaction is completed, take out the carbon nanofiber paper CNFs, wash it with deionized water, and dry it naturally to obtain the pretreated carbon nanofiber paper CNFs, which is used as the working electrode in the three-electrode electrochemical system.

[0049] The Pt counter electrode and the Ag / AgCl reference electrode are used together with the working electrode to form a conventional three-electrode electrochemical system. The Zn(NO3)2 solution is heated and maintained at 70°C as the electrolyte.

[0050] The electrochemical impedance spectroscopy (EIS) of the electrolyte on the CNFs paper is characterized, and the frequency range is 0.1 Hz to 100,000 Hz. For comparison, the EIS scanning of the electrolyte with the same concentration on the sputtered Au / Si substrate is also measured. Subsequently, the CNFs paper and the Au / Si sample are respectively subjected to cyclic voltammetry (CV) test. It is found that, at the same scanning rate, the CV curve of the CNFs paper electrode encloses an area much larger than that of the Au-Si electrode, reflecting that it has a larger charge storage capacity and a higher specific capacitance, and is more prone to deposit zinc oxide. In addition, when the CNFs paper electrode is scanned from the open circuit potential 0.84V to the negative direction, the current density rapidly rises to 5.3mA*cm -2 at-0.26V, and then slowly grows to 7.29mA*cm -2 at-1.11V.; a rapid reduction current (corresponding to metal deposition) appears below -1.11 V, and then the current returns to zero at -0.8 V. The current density is almost zero before -0.33 V, and only when the potential is further negatively shifted (more than -0.33 V) does an appreciable current appear, indicating that only under a stronger driving electric field can the limited active surface participate in charge transfer. The experimental results confirm that in order to achieve the purpose of selective deposition pulse voltage, a potential lower than -1.11 V should be used as the opening potential.

[0051] Then, under the conditions that the opening potential is -1.7 V, -1.8 V or -1.9 V, the closing potential is -0.8 V, and the ratio of opening to closing time is 1:1, 1:5, 1:10, 1:20, 1:50, 1:100 respectively, micro-nano powders are obtained on the surface of carbon nanofiber paper CNFs by electrochemical pulse deposition method, marked as samples 1-9, and the corresponding parameters of each sample are shown in Table 1.

[0052] Table 1 Electrochemical pulse deposition parameters corresponding to each sample

[0053] Sample No. Open potential Close potential Time ratio of open to close 1 -1.7 V -0.8V 1:5 2 -1.7 V -0.8V 1:50 3 -1.7 V -0.8V 1:100 4 -1.8 V -0.8V 1:20 5 -1.8 V -0.8V 1:50 6 -1.8 V -0.8V 1:100 7 -1.9 V -0.8V 1:10 8 -1.9 V -0.8V 1:50 9 -1.9 V -0.8V 1:100

[0054] Each sample is detected by X-ray diffractometer, and the XRD patterns of samples 3, 4 and 8 are shown in Figure 3. The results show that under the conditions of the parameters listed in Table 1, zinc oxide crystal structures can be deposited.

[0055] Each sample is observed under an electron microscope, and the particle size distribution of each sample is 200 nm-2 μm. It can be observed that different deposition parameters affect the crystal structure of the obtained powder, and it is speculated that these different crystal structures may affect the optical properties of the powder.

[0056] In order to further verify their optical properties, the photoluminescence spectra of different samples are tested. The opening potential is selected as -1.8 V, the closing potential is -0.8 V, and the ratio of opening to closing time is set as 1:1, 1:5, 1:10, 1:20, 1:50, 1:100 respectively. Samples are prepared in the same way. Under the excitation light of 350 nm and 550 nm-600 nm, only the samples with the opening to closing time ratio of 1:1, 1:5 and 1:20 can emit fluorescence, as shown in Figure 3-2.

[0057] Example 2 Applied to the surface of aluminum foil material

[0058] A small amount of sample 4 powder prepared in Example 1 is evenly covered on the fingerprinted aluminum foil, the latent fingerprint area is irradiated with 450 nm blue light and photographed, and the experimental results are shown in Figure 4-1. The clear papillary lines, fingerprint triangles and other detailed features are obvious.

[0059] Example 3 Application to the surface of wooden material

[0060] A small amount of the sample 4 powder prepared in Example 1 was evenly covered on the fingerprinted wooden table top, the latent fingerprint area was irradiated with 530 nm green light and photographed, and the experimental results are shown in Figure 4-2. It can be seen that the clear papillary ridge lines, fingerprint triangles and other detailed features are obvious.

Claims

1. A method for preparing electrochemically pulsed deposited zinc oxide micro-nano powders, the method comprising the following steps: (1) Pretreatment of carbon nanofiber paper (CNFs) Clean carbon nanofiber paper (CNFs) was immersed in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid for 4 hours. After being removed, it was thoroughly rinsed with deionized water to obtain pretreated carbon nanofiber paper (CNFs). (2) Configure a three-electrode electrochemical system A three-electrode electrochemical system was constructed by Pt counter electrode, Ag / AgCl reference electrode and pretreated carbon nanofiber paper CNFs working electrode, with Zn(NO3)2 solution as electrolyte. (3) Electrochemical pulse deposition Zinc oxide micro-nano powders were obtained on the surface of carbon nanofiber paper (CNFs) by electrochemical pulse deposition under conditions of electrolyte heating, with an on-potential of -1.7 V to -1.9 V, an off-potential of -0.8 V, an on-to-off time ratio of 1:(1~100).

2. The preparation method according to claim 1, characterized in that... The cleaned carbon nanofiber paper (CNFs) was washed with acetone, alcohol, and deionized water, respectively.

3. The preparation method according to claim 1, characterized in that... The mixed acid solution in step (1) contains concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, wherein the mass percentage of concentrated sulfuric acid is 98% and the mass percentage of concentrated nitric acid is 68%.

4. The preparation method according to claim 1, characterized in that... In step (2), the electrolyte has a pH of 5.26 and a concentration of 0.05 mol / L.

5. The preparation method according to claim 1, characterized in that... In step (3), zinc oxide micro-nano powders were obtained on the surface of carbon nanofiber paper CNFs by electrochemical pulse deposition under the conditions of -1.8 V on-state potential, -0.8 V off-state potential, on-state to off-state time ratio of 1:(1~20) and 70℃.

6. The zinc oxide micro-nano powder prepared by the preparation method of any one of claims 1-4, wherein the zinc oxide micro-nano powder has a particle size distribution of 200 nm to 2 μm.

7. The application of zinc oxide micro-nano powder as described in claim 6 in latent fingerprint development.

8. A method for developing latent fingerprints using zinc oxide micro-nano powder, the method comprising the following steps: (1) Zinc oxide micro-nano powder is attached to an object with latent fingerprints; (2) Irradiate the area on the object to which zinc oxide micro-nano powder is attached with excitation light to obtain a latent fingerprint image.

9. The method according to claim 8, characterized in that... The object includes articles made of wood or metal.

10. The method according to claim 8, characterized in that... The excitation wavelength is 350nm~700nm.

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